This application is directed to optically coupling a high brightness light source to a remote end use via a light conductor and, more particularly, to an optical system that provides improved light mixing and more uniform light intensity and color.
The invention is particularly applicable to optical systems of the type as shown and described in U.S. Pat. No. 5,341,445--Davenport, et al.; 5,469,337--Cassarly, et al.; and 5,691,696--Mazies, et al. The details of the '445; '337; and '696 patents are incorporated herein by reference. Generally, these patents disclose a high brightness light source, for example one measuring in excess of 50,000 lumens per square centimeter, associated with a reflector arrangement that inputs light to one or more optical light conductors, pipes or fibers. Light enters the individual light fibers through suitable coupling members which collect light that would normally fall outside of an input surface area of a light fiber and exits at an opposite end thereof for use at a remote location.
Selected applications of these types of systems require a light fiber to undergo a tight bend, for example, when turning a corner. A commercial embodiment exhibiting this requirement is an automotive lighting system where the light source is located in a central location such as under the engine hood. The headlights are located on either side of the engine compartment and directed forwardly of the vehicle, thus, necessitating that the light fibers undergo a bend or turn to direct the light in a forward direction.
This bend of the light fibers can approach 105 degrees in a small area, for example, a two-by-two inch box which adversely affects optical transmission. Heretofore, such a tight bend would adversely impact on light output from the headlamp system. Intensity or angular distribution and illuminance or spatial distribution are both impacted. Ideally, the turn must be accomplished with no significant loss and no significant increase in the angular distribution.
By of way of example, a Teflon clad light fiber of a diameter of 0.5 inches is difficult to bend through a small radius in a headlamp assembly. The cladding surrounding the core material starts to kink at a bend radius of approximately four inches. Moreover, brightness significantly decreases at a bend radius of about seven inches.
One attempt to solve these problems was to remove the cladding from a portion of the fiber in the bend region. Without the cladding, negligible light was lost but the angular distribution was still severely distorted. The main portion of light exiting the light fiber was shifted by about ten degrees, a dark spot was found on-axis, and significant radiant energy was thrown to higher angles. This led to an unacceptable reduction in both peak candelas and total lumens out of the headlamp.
Yet another problem associated with high intensity discharge light sources is significant color separation. Typically, the light has a red perimeter with a white interior portion as described in the '445patent. One proposed solution to the color separation as disclosed in the '445 patent is to use a square coupler. The square coupler provides for mixing of the intensity and color of the light as it travels through the square coupler. The polygonal-shaped square coupler provides an increased number of internal reflections per unit length thereby achieving a more uniform distribution of the light intensity and improved color mixing over that achieved with a standard, cylindrical tubular coupling member.
Color separation is also a problem when two independent light sources are used. For example, where two independent sources are used, there are presently no solutions that provide high performance, i.e., long life, minimal complexity, maximum beam lumens, and minimal color separation.
Accordingly, a need exists to address these problems in an inexpensive and effective manner.